Post written by Mitsuru Nagata, MD, from the Department of Endoscopy, Shonan Fujisawa Tokushukai Hospital, Kanagawa, Japan.

We present a case of a duodenal tumor that was treated by underwater ESD using a bent-type knife (Hook Knife J) and discuss potential advantages of underwater ESD.

Most studies on underwater ESD involved the use of only a straight needle-type knife in saline solution. However, in situations such as vertical position opposite the muscle layer, poor maneuverability of the endoscope, and severe fibrosis, submucosal dissection by use of a straight needle-type knife sometimes becomes difficult because of an increased risk of perforation. Therefore, an approach other than one involving a straight needle-type knife is needed in underwater ESD, as in conventional ESD.

When the Hook Knife J (bent-type knife) is used in saline solution, it is necessary to change the electrosurgical unit settings from that of conventional ESD because of the high electrical conductivity of saline solution. We described the details of the use of a Hook Knife J in saline solution including the electrosurgical unit settings.

Endoscopists should be aware of the “visible range change” resulting from underwater conditions. Basically, once air is replaced by water, the focal length increases, and far objects may appear closer. We coined this effect as “elongation of reach,” which may offer an advantage in specific situations.

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